array_key_exists 能檢查多維數組中的鍵嗎？具體該怎麼用？

gitbox 2025-09-12

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// --------------------</span></span><span>
</span><span><span class="hljs-comment">// 這裡是與文章內容無關的 PHP 代碼示例</span></span><span>
</span><span><span class="hljs-variable">$dummyArray</span></span><span> = [</span><span><span class="hljs-number">1</span></span><span>, </span><span><span class="hljs-number">2</span></span><span>, </span><span><span class="hljs-number">3</span></span><span>];
</span><span><span class="hljs-keyword">foreach</span></span><span> (</span><span><span class="hljs-variable">$dummyArray</span></span><span> </span><span><span class="hljs-keyword">as</span></span><span> </span><span><span class="hljs-variable">$value</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$value</span></span><span> * </span><span><span class="hljs-number">2</span></span><span> . </span><span><span class="hljs-string">"\n"</span></span><span>;
}
</span><span><span class="hljs-comment">// --------------------</span></span><span>
</span><span><span class="hljs-meta">?&gt;</span></span><span>

---

</span><span><span class="hljs-comment"># array_key_exists 能檢查多維數組中的鍵嗎？具體該怎麼用？</span></span><span>

在 PHP 中，`array_key_exists` 函數用於檢查一個數組中是否存在指定的鍵。它的基本用法如下：

```php
</span><span><span class="hljs-variable">$array</span></span><span> = [
    </span><span><span class="hljs-string">'name'</span></span><span> =&gt; </span><span><span class="hljs-string">'Alice'</span></span><span>,
    </span><span><span class="hljs-string">'age'</span></span><span> =&gt; </span><span><span class="hljs-number">25</span></span><span>
];

</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">array_key_exists</span></span><span>(</span><span><span class="hljs-string">'name'</span></span><span>, </span><span><span class="hljs-variable">$array</span></span><span>)) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"鍵 'name' 存在"</span></span><span>;
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"鍵 'name' 不存在"</span></span><span>;
}
</span></span>

運行結果：

 <span><span>鍵 </span><span><span class="hljs-string">'name'</span></span><span> 存在
</span></span>

一、array_key_exists 與多維數組

需要注意的是， array_key_exists只能檢查當前數組層級的鍵，它不會自動遞歸檢查多維數組中的嵌套鍵。例如：

 <span><span><span class="hljs-variable">$multiArray</span></span><span> = [
    </span><span><span class="hljs-string">'user'</span></span><span> =&gt; [
        </span><span><span class="hljs-string">'name'</span></span><span> =&gt; </span><span><span class="hljs-string">'Bob'</span></span><span>,
        </span><span><span class="hljs-string">'email'</span></span><span> =&gt; </span><span><span class="hljs-string">'[email protected]'</span></span><span>
    ]
];

</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">array_key_exists</span></span><span>(</span><span><span class="hljs-string">'user'</span></span><span>, </span><span><span class="hljs-variable">$multiArray</span></span><span>));        </span><span><span class="hljs-comment">// true</span></span><span>
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">array_key_exists</span></span><span>(</span><span><span class="hljs-string">'name'</span></span><span>, </span><span><span class="hljs-variable">$multiArray</span></span><span>));        </span><span><span class="hljs-comment">// false</span></span><span>
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">array_key_exists</span></span><span>(</span><span><span class="hljs-string">'name'</span></span><span>, </span><span><span class="hljs-variable">$multiArray</span></span><span>[</span><span><span class="hljs-string">'user'</span></span><span>])); </span><span><span class="hljs-comment">// true</span></span><span>
</span></span>

上面的例子說明：

'user'是$multiArray的頂層鍵，所以檢查返回true 。
'name'並不是$multiArray的頂層鍵，所以直接檢查返回false 。
如果想檢查嵌套數組中的'name'鍵，需要先訪問$multiArray['user']再調用array_key_exists 。

二、檢查多維數組中的鍵的方法

如果你想在多維數組中遞歸檢查某個鍵是否存在，可以自己寫一個輔助函數：

 <span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">array_key_exists_recursive</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-variable">$key</span></span></span><span>, </span><span><span class="hljs-variable">$array</span></span><span>) {
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">array_key_exists</span></span><span>(</span><span><span class="hljs-variable">$key</span></span><span>, </span><span><span class="hljs-variable">$array</span></span><span>)) {
        </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-literal">true</span></span><span>;
    }

    </span><span><span class="hljs-keyword">foreach</span></span><span> (</span><span><span class="hljs-variable">$array</span></span><span> </span><span><span class="hljs-keyword">as</span></span><span> </span><span><span class="hljs-variable">$value</span></span><span>) {
        </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">is_array</span></span><span>(</span><span><span class="hljs-variable">$value</span></span><span>) &amp;&amp; </span><span><span class="hljs-title function_ invoke__">array_key_exists_recursive</span></span><span>(</span><span><span class="hljs-variable">$key</span></span><span>, </span><span><span class="hljs-variable">$value</span></span><span>)) {
            </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-literal">true</span></span><span>;
        }
    }

    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-literal">false</span></span><span>;
}

</span><span><span class="hljs-comment">// 示例</span></span><span>
</span><span><span class="hljs-variable">$multiArray</span></span><span> = [
    </span><span><span class="hljs-string">'user'</span></span><span> =&gt; [
        </span><span><span class="hljs-string">'name'</span></span><span> =&gt; </span><span><span class="hljs-string">'Bob'</span></span><span>,
        </span><span><span class="hljs-string">'email'</span></span><span> =&gt; </span><span><span class="hljs-string">'[email protected]'</span></span><span>
    ],
    </span><span><span class="hljs-string">'settings'</span></span><span> =&gt; [
        </span><span><span class="hljs-string">'theme'</span></span><span> =&gt; </span><span><span class="hljs-string">'dark'</span></span><span>
    ]
];

</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">array_key_exists_recursive</span></span><span>(</span><span><span class="hljs-string">'email'</span></span><span>, </span><span><span class="hljs-variable">$multiArray</span></span><span>)); </span><span><span class="hljs-comment">// true</span></span><span>
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">array_key_exists_recursive</span></span><span>(</span><span><span class="hljs-string">'theme'</span></span><span>, </span><span><span class="hljs-variable">$multiArray</span></span><span>)); </span><span><span class="hljs-comment">// true</span></span><span>
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">array_key_exists_recursive</span></span><span>(</span><span><span class="hljs-string">'age'</span></span><span>, </span><span><span class="hljs-variable">$multiArray</span></span><span>));   </span><span><span class="hljs-comment">// false</span></span><span>
</span></span>

這個函數會遍歷數組中的每一層，如果找到了指定的鍵就返回true ，否則最終返回false 。

三、總結

array_key_exists默認只檢查當前數組層級的鍵。
多維數組中嵌套的鍵，需要先訪問對應的子數組，或者使用遞歸函數。
使用遞歸方法可以方便地檢查多層數組中是否存在某個鍵，非常適合配置數組或複雜數據結構。

通過這種方法，你可以更靈活地處理多維數組中的鍵檢查，而不會被array_key_exists的局限性所困擾。

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array_key_exists